1998年中国長江の洪水災害について

Abstract

1998年の7月から8月にかけて中国の長江で大洪水が発生した.洪水の原因は異常な豪雨にあるが, 亜熱帯高圧帯が長江に沿って移動し, 下流の洪水流出と上流のそれとが重畳したこと, 洞庭湖・ポーヤン湖の容積が減少したために洪水調節能力が低下したこと, 洪水の疎通能力を低下させるような輪中や建物が堤外地に多数造られたこと, 河床上昇により洪水規模の割には水位が高くなったこと等により, 長期間の高水位を持続し, 本川堤防の決壊や輪中堤の決壊, 多数のパイピングや漏水等が発生した.ここでは, 今回の洪水の原因と特徴, 被害の概要, 長江の治水計画, 洪水対策等について報告する。

A great flood occurred at the Changjiang River, China in July and August, 1998. The primary cause of the flood is an extraordinary heavy rainfall brought by the subtropical high which moved along the Changjiang River. Owing to the rainfall, a flood runoff at the upstream fell on the runoff at the downstream, resulting in the great flood of a long duration. The decrease of water storage capacity of the Dongting Lake and Poyang Lake due to reclamation also magnified the flood scale.A flood water level was higher comparing the flood water discharge due to decrease of flood discharge capacity by the construction of a large number of buildings and circle levees which are called as "yuan" in Chinese in the riverside lands, as well as due to aggradation of the river bed. In this paper, the results obtained by the hearing and the field survey concerning the cause of the great flood, flood control planning of the Changjiang River, the aspects of flood and flood disasters, and countermeasures in future, are reported.